HackerRank/Algorithm/SimpleTextEditor kotlin

SimpleTextEditor.kt

import java.util.*

class TextEditor(initialValue: String = "") {

    private val operationHistory = Stack<String>().apply { push(initialValue) }
    val value: String
        get() = operationHistory.peek()

    fun append(text: String) {
        operationHistory.push(operationHistory.peek() + text)
    }

    fun delete(count: Int) {
        operationHistory.push(value.dropLast(count))
    }

    fun print(number: Int) {
        println(value[number - 1])
    }

    fun undo() {
        operationHistory.pop()
    }
}

const val OP_APPEND = 1
const val OP_DELETE = 2
const val OP_PRINT = 3
const val OP_UNDO = 4

fun editText(
    operations: LinkedList<Pair<Int, String?>>,
    scanner: Scanner,
): String {
    val editor = TextEditor()
    operations.forEach { operation ->
        when (operation.first) {
            OP_APPEND -> {
                editor.append(operation.second!!)
            }

            OP_DELETE -> {
                editor.delete(operation.second!!.toInt())
            }

            OP_PRINT -> {
                editor.print(operation.second!!.toInt())
            }

            OP_UNDO -> {
                editor.undo()
            }
        }
    }

    return editor.value
}

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    val operations = LinkedList<Pair<Int, String?>>()
    repeat(scanner.nextLine().toInt()) {
        val operationInput = scanner.nextInt()

        operations.add(
            operationInput to if (operationInput.hasAdditionalInput) {
                scanner.next()
            } else {
                null
            },
        )
    }

    editText(
        operations = operations, scanner = scanner
    )
}

val Int.hasAdditionalInput: Boolean
    get() = when (this) {
        OP_APPEND, OP_DELETE, OP_PRINT -> true
        OP_UNDO -> false
        else -> throw IllegalArgumentException()
    }